1. Field of the Invention
The present invention relates to a sintered sliding member, in particular a sliding member for high temperatures, and a production method thereof.
2. Description of the Related Art
As a sliding member used under high temperatures, a sintered sliding member comprising an ironbased alloy matrix containing chromium, for instance, metal alloy such as stainless steel, excellent in thermal resistance and oxidation resistance, into which matrix are distributed solid lubricants such as carbon or h-BN (hexagonal boron nitride particles), is known in JP-A-54-128923 Publication and JP-A-60-221557 Publication.
In JP-A-60-215736 Publication, JP-A-2-290905 Publication and JP-A-4-191343 Publication, there are disclosed inventions in which the pore of sintered body is infiltrated with copper to thereby promote the mechanical strength and oxidation resistance.
According to the invention disclosed in JP-A-60-215736, a compact is formed with alloy steel powder (matrix material) containing 2.5 to 25 wt. % chromium and 0.2 to 3.0 wt. % carbon, the compact being then sintered at a temperature higher by 0 to 50.degree. C. than the liquid phase-occurring temperature of the alloy steel powder while it is kept in contact with copper-based metal so that the copper-based metal is infiltrated into the compact, thereby obtaining a sintered alloy excellent in wear resistance.
In JP-A-2-290905 Publication, there is disclosed a sliding member produced by the steps of mixing metal powder and a solid lubricant such as graphite, compacting and sintering the mixture to thereby obtain a compact, and infiltrating a low melting-point metal such as copper into the compact to thereby produce the sliding member.
In JP-A-60-215736 Publication among the conventional techniques mentioned above, however, a compact is made of alloy steel powder containing 0.2 to 3.0 wt. % of carbon. In this compact, carbon is chemically combined with chromium during sintering to thereby become very hard chromium carbides, which hard carbides are precipitated into the matrix of alloy steel to thereby achieve the enhancement of wear resistance. In consequence, the hard carbides increase the attacking property against a mated member, so that the application thereof to a soft mated member especially of not more than 300 Hv has been difficult.
Further, in JP-A-2-290905 Publication, since no chromium acting as a carbide forming element is contained and since graphite of as large an amount as 10 wt. % is mixed in, the added graphite does not become hard carbides and free graphite exists. That is, this conventional technique is intended to improve the sliding characteristics such as frictional coefficient by using the free graphite as a solid lubricant. Thus, when used in the oxidation atmosphere, free graphite is rapidly oxidized, so that this technique was inapplicable as a sliding member for high temperatures.